Many situations exist in which condition monitoring of an electrical machine is required, for example to detect and diagnose faults. Clear detection of faults is highly desirable, in order to identify them before they become unacceptable, and to minimise the risk of catastrophic failure during machine operation. The diagnosis of a forthcoming fault event is desirable to allow a better understanding of the fault, to allow appropriate spare parts to be available before the machine is dismantled for repair, and to identify the appropriate parts of the machine to dismantle for repair.